Thursday, December 1, 2011

How to Grow Green Algae on Rocks

Algae grow readily on damp rocks.

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Algae on rocks need not always be a slippery pest. Green algae on rocks around a water feature make it look older and more rustic. In a pond or aquarium, algae provide grazing opportunities for fish, mollusks and tadpoles. Algae are resilient organisms with simple needs. The provision of moisture and nutrients usually promotes the growth of all the algae you could want.

Related Searches:Difficulty:Moderately EasyInstructions Things You'll NeedRiver rocksPlant misterSeaweed fertilizer5- or 10-gallon tankOrganic houseplant fertilizerBucketsSuggest EditsAround a Pond1

Position river rocks around the pond in positions that receive plenty of light but not necessarily direct sunlight.


Spray or paint the rocks with a solution of seaweed fertilizer and water. Use the strength recommended on the packaging for most plants or a slightly stronger solution.


Mist the rocks with rainwater daily. The key to encouraging algae growth is moisture. If the rocks dry out quickly, move them to a shadier location.


Apply more of the fertilizer solution once or twice a week until the rocks have the desired appearance. After this, leave the algae to take care of themselves.

For Aquarium Fish1

Set up a small tank with dechlorinated water and all the rocks you wish algae to grow upon.


Position the tank in a well-lit location or switch on a powerful aquarium light for 12 hours a day.


Add a little organic houseplant fertilizer to the water once a week.


Conduct occasional water changes to control the growth of free-floating phytoplankton, which compete with the attached algae for nutrients and light. Replace about 25 percent of the water with fresh dechlorinated water once a week before adding fertilizer.


Transfer rocks to the main tank or pond once they have sufficient algal growth. Replace each rock with a new one if you want a continuous supply of algae.

Tips & Warnings

Dechlorinate tap water by leaving it in buckets for 24 hours. Alternatively, use a commercial dechlorinator from an aquarium supply store. Note that neither method will remove chloramine. If your water supply contains this chemical, ask an aquarium supplier for the appropriate treatment.

Although adding nutrients, especially phosphorus and nitrogen, to a pond encourages the growth of algae on rocks, this practice is best avoided. These nutrients also promote the growth of free-floating phytoplankton, another type of algae. Phytoplankton blooms can reduce oxygen levels, block light to submerged plants and, in the worst cases, kill aquatic life. Let underwater algae establish themselves.

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ReferencesAquatic Community: Algae in AquariumsMinnesota Department of Natural Resources: What’s That Green Stuff?Photo Credit Jupiterimages/ ImagesRead Next:

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